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What is carbohydrate loading?

Carbohydrate loading is a concept that both athletes and the general pubic know of. This is largely due to the marketing of carbohydrate based products such as whole grains, sugary snack foods and sports drinks being the champion or elite sports performance, and in some part to information passed on via successful ex-elite athletes extolling the virtues of the dietary regimens that propelled them to the top of their sport. The concept of carb loading for the London marathon to improve performance has been so successful that people think they need to carb load for all and any sports, however this is not the case!

How do I card load for a marathon?

Carbohydrate loading for the London Marathon is a strategy employed by athletes that involves reducing training volume whilst simultaneously increasing the amounts of carbohydrates consumed in the days leading up to a game or event such as the London Marathon. The aim is to up regulate an enzyme called glycogen synthase (an enzyme that creates muscle fuel called glycogen) and cause the muscles to store higher than normal levels of glycogen. Muscle glycogen stores are normally about 100-120mmol/kg BW, but with carbohydrate loading they can reach 150-225mmol/kg BW.

Carbohydrate loading was originally developed in the 1960’s by Scandinavian researchers and involved a complicated 6-7 day period of a “depletion phase” – essentially a low carbohydrate diet – in conjunction with several hard training sessions. The aim of this phase was to deplete muscle glycogen stores and excite the enzyme glycogen synthase. Muscle glycogen stores could fall to as little as 25mmol/kg BW. This was then immediately followed by a 3-4 day “loading phase” where athletes would consume a very high carbohydrate diet (anywhere from 7-12g of carbohydrate per kg BW) whilst tapering exercise leading up to the event. However this approach to carbohydrate loading had its problems with athletes reporting muscle weakness, fatigue, anxiety and irritability.

Carbohydrate loading evolved thanks to research out of Ball State University, Indiana, whereby the depletion phase was found to be unnecessary. Now athletes are advised that they don’t need to complete the “depletion phase” and only need to slowly taper exercise and to eat a high carbohydrate diet in the 3-4 days leading up to an event.

Consider an example below of a high carbohydrate diet from the Australian Institute of Sport (AIS) suitable for a 70kg athlete providing 630g of carbohydrate, 125g of protein and 60g of fat:


3 cups of low-fibre breakfast cereal with 1½ cups of reduced fat milk
1 medium banana
250ml orange juice


Toasted muffin with honey
500ml sports drink


2 sandwiches (4 slices of bread) with filling as desired
200g tub of low-fat fruit yoghurt
375ml bottle of soft drink


Banana smoothie made with low-fat milk, banana and honey
cereal bar


1 cup of pasta sauce with 2 cups of cooked pasta
3 slices of garlic bread
2 glasses of cordial

Late Snack

Toasted muffin and jam
500ml sports drink

This type of diet is a low protein, low fat, low fibre diet high in carbohydrates. The trouble with carbohydrate loading is that many people get it wrong – they use it as an excuse to eat anything they want, usually food laden with fat as well as sugar, but you can see from the example above that the food consumed should be low fibre, high glycemic load sugary, starchy foods – not fatty junk food.

Herein lies another problem – this food is not very good for the teeth; it’s certainly not very good for blood sugar control and could lead to excess body fat accumulation if done too regularly, and it may lead to high triglycerides, gout or liver damage that have all been associated with consuming high amounts of fructose, high fructose corn syrup and sugar in general.

What do we need for performance?

In the example from the AIS above the foods, although high in carbohydrates, are also low in nutrition. Consider the kerbs’ cycle and electron transport chain (I can see your eyes glazing over here but bear with me). You don’t need to understand all the chemical reactions, just the fact that in order to turn all the carbohydrate in to energy you need a whole host of vitamins and minerals such as B vitamins, vitamin C, magnesium, CoQ10, copper, iron and sulphur. So it would be wise to consume foods like whole grain rice, dried fruit, sweet potato etc… that have carbs, but also have nutrients in them.

How to prepare for the London Marathon

Carbohydrate loading should be done for 3-4 days prior to the London Marathon as outlined by the AIS, and after having completed the event eat normally again. It might still be wise to consume some more nutrient dense carbohydrates foods such as tropical fruit, dried fruit, starchy vegetables and whole grains instead of foods such as jam, honey and muffins.

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